Ion-exchange processes for the treatment of water



NOV. 11, 1952 R EMMETT ET AL 2,617,766

IONEXCHANGE PROCESSES FOR THE TREATMENT OF WATER Filed Dec. 5, 1950 PM Email 2% 24% fiazflewa 5M wh m This invention relates Patented Nov. 11, 1952 UNITED STATES PATENT OFFICE),

ION -EXGHAN GE PROCESSES FOR THE TREATMENT OF WATER James Ratcliffe Emmett, Cranham, Upminster, and Henry Alfred Matthews, Hayes, England, assignors to Ewbank and Partners Limited, London, England, a company of Great Britain Application December 5, 1950, Serial No. 199,202

In Great Britain December 8, 1949 to ion-exchange processes for the treatment of water in which the rawwater is passed in succession through a unit (the cation unit) containing a cation exchange material, such for example as sulphonated coal or sulphonated phenol-formaldehyde resins, and a unit (the anion unit) containing an anion exchange material, such for example as an amino-aldehyde resin, and in which the active materials are intended to be regenerated from time to time, when exhausted or substantially so, by running through each of the units a solution of a suitable regenerant chemical (an acid, for example, for the cation unit and an alkali, for

example, for the anion unit) while the supply of regeneration. Analytical tests still had to be carried out in order to determine which unit had exhausted and if this proved to be the cation unit the waterin the anion unit, not being completely decationised; had to be discharged to waste Still later,- however, instruments for measuring differential conductivity values between partially decationised water and completely decationised water wereadopted so that an indication could be secured of the exhaustion of the cationunit, the instrument for measuring, the conductivity of the water. leaving the anion unit then serving to? indicate exhaustion of the'anion unit only.

Processesand plants operated in accordance with theselatest refinementsrequire much less labour for their operation than those initially installed butstill suffer-from. a disadvantage in those cases, which are quite numerous, where the ratio between thebicarbonate alkalinityand the total ionised solids content of the water to be treated variesfrom the accepted value by even small amounts. These changes cause the anion and cation units to require regeneration at differenttimes whereas they would both be exhausted together if the ratio referred'to remained. at thev accepted value. r

Forexample, in a typical'case where the water 4 Claims. (Cl. 210-24) has a bicarbonate alkalinity of 200 parts per million (calculated as CaCOs) and a total ionised solids content of 400 parts per million (calculated as CaCOc), a plant for treating this water at a rate of 1,000 gallons per hour would comprise 28.0 cubic feet of a cation exchange material having a capacity of 8,000 grains per cubic foot and 11.2 cubic feet of an anion exchange material having a capacity of 10,000 grains per cubic foot. The period between regenerations would be 8 hours'and the time required for regenerating either unit alone would be about 1.25 hours (for both together it could be effected in about 1.5

hours).

Shouldthe bicarbonate alkalinity of the water increase to 225 parts per million (as 'CaCOa), and the total ionised solids decrease to 375 p. p. m., the period between regenerations of the cation unit would be increased to 8.5 hours but the period between regenerations of the anion unit would be increased to 10.7 hours.

The alternatives available to the operating personnel would be (1) to regenerate each unit in turn as it became exhausted or (2) to regenerate both units when the cation unit became exhausted. The first course would entail shutting down the plant for a period of 2.5 hours in each periodof 13.2 hours, with the personnel engaged for 2.5'hours, and the second course would reduce the shut-down period to 1.5 hours in each period of 10 hours but with a wastage of the regenerant chemical employed for the anion unit amounting to approximately 20%, since the full amount would have to be used because the degree of exhaustion of the unit would not be known.

It is the object of the present invention, therefore, to provide an improved method of and means for use in operating a process of the character referred to above whereby the twounits may be regenerated simultaneously without waste of regenerant chemicals.

According to this invention a method of operating an ion-exchange process for the treatment of water includes the steps of continuously measuring the conductivity of the decationised water prior to its entry into the anion unit, continuously measuring the rate of flow of the Water through the'unit, automatically combining the indications thus obtained to produce a continuous indication of the degree of exhaustion of the anion exchange material, and determining thequantity of the regenerant chemical to be employed in accordance with the value of the last-mentioned indication at the time when the anionunit is to be regenerated.

The invention also consists in apparatus for treating water by an ion-exchange process, including a cation unit and an anion unit to be traversed in succession by the water to be treated, wherein. .means is vprovided for "measuring .the conductivity of the 'water flowing from thezcation unit to the anion unit, means is provided for measuring the rate of flow of this water and further means is provided for integrating the indications of the first two means -inn-ordei to produce an indication varying with "the degree of exhaustion of the anion exchange lmaterial.

One way of carrying thednventioniinto practical efiect will now be described withl.reference to the accompanying drawing, ithessingle fi ure a of which is a diagrammatic representation of a water treatment plant with-the known-.meansfor efiecting backwashing and regeneration of the units omitted.

In the example illustrated, the cation and qanion @units' of 2 a plant for treating water-by tan "ion-exchange process are arrangedon the .usual .afashionand provided with the known-instrumentation :referred ;to above vwhereby -.the --substan- .Qtiallycomplete exhaustion of the cation exchange 2 material or. ofnthe anion--exchangeematerial vma ihesseparately notifiedito the operating personnel gintan :automatic .,manner. as and "when it occurs. {there is additionally z provided,.- -in iaccordanee zwith ,this invention, an instrument *which con- -sented by the conductivity meters 8, 8 and I6,

.. the;plant accordingto this invention is provided withran:instrument (meter it) which continu- -'pns l y:measures'gthe electrical conductivity of the :decationised'water flowing to the anion unit l2 and anuinstrument (flow meter M) which con- -;tinuous1y measures the rate of flow of this water tinuously :measures both the electrical -conduc- I -rtivity--;of aand the rate. of ifiow of the decationised :zwater flow-mg .,to the :anion-unit and integrates the indications produced so that it causesz-the movement 10f a :member by an :amount which a yarieswith the: degree of exhaustion of the-anion egexchange rma-terial.

' "The cation unit :COIIlpIiSQS 'a wessel I contain- :ing;.-a-suitable cation-.exchange -material (not :shown), such as sulphonated coal,:. and-is supplied with the ,rawwater .to 'be treated -loyn-wa ;:of ;a "pipe .2. -:A small but :const-ant proportion of =the -:r aw water is :bled-off :from .the pipe 6-2 by means :01 z-pipe :3 and 515 conducted thereby "into l-ran e auxiliary Nessel 14 gcontaining arquantity of :zthe eSfiIIlGrgGfiblQIl exchange material as is placed in :thevessel -;l this uantity :being so --.determined zthat. it will never be vexhausted before the. materialgin zthB vessel I iszexhausted. 1 The decationfised-water leaving :the vessel 1 conducted by :a ,pipe -5 to. an iinstrumentqfi .(;of: knowntype). for "measuring :the electrical conductivity --of this water, and the edecationised water .:.leaving the wessel :4 is1similar1y ,conducted: by ;.a :pipe 51 ,to .:a

similar econductivity water 8. --o1':met.ers ;8,::ar.e-: associated: in the tknownimanrner so thatea:decrease1initheconductivity of-the water; leaving :the wessel ll inwmlation: tothe:.con- .iductivity of:;the water leaving the-vessel 4 will anrodueewan indication, m1 give ;an :aud-ible hr x The instruments through the anion unit. As indicated by the broken lines I8 and IS, the outputs of the meters 10 and I4 are respectively connected to an inte- Hgrating instrument :20 in ;;order to cause move- ;mentpf .its gpointer 21. over a :calibratedscale 22 by angamount-whieh ivar-ies with the. degree of exhaustion :of .the -an-ion exchange material the unit .42.

The conductivity of the -decationised "water rflowingtthrough the meter Hl is almost entirely due to thepresence'of sulphuric-and hydrochloric acids in a solution therein andthe mobilities :of .thesulphate .-.and .ch1oride;.-ionsare. sufiiciently .close eto :each (other eto eensure that lthere will :be rbuteatnegligibleverror inadopting .a relationship between ;conductivity 2 of -.the :decation-ised water :and ixeguivalent rconcentrat-ion 10f the two :acids therein \which :is ;correct for one :onlycdf :those acids. At,theconcentnations,concerned,:thisrela- .1tionship is :sufiiciently close to a linear zone so rthat'integrationzof the measurementspfsth'e conductivity ,gives a 'measu-re 13f the concentration -.of ethe e-a-cidsin the watenfiowing .to the :anion xunit :and (this appropriately :combined with the rvolume --:of i the water which i has :flowed :into :the unit .;-sinee :run @was .started yieldstz thetrtotal weighteof thezaci'dswhich i-haxzezenteredtthe duri-ngfthe "run. .Gonsequentlyflthe movementcdf theapointer 12 l operated by :rthe'inst-rument" .2ll;.is -proportional ;to (the degreexof exhaustion-of c-the ;-a-nion :iexch-angezmaterialriand 113116586218 322 rmay :be ccalibratefd :in npounds :weight of :regenerant rc'hexnicalgdue to iallowance being .imade :forfithe :regenerantlefficiency.

When: thezcationnin'it I is;exhausterl,xtherefore, fitfis a :simple' matter :to :=regenerate':both mnits l and 1-2 atzthe samesitime, :the quantity of the :gregenerant :chemical :used \for .the :anion :unit 12 11b sing: .determine'diiriaccordance with the.-position ear :the ip'ointe'rtsz l :relativeito the 'scale; 22.

."zTheres arezmany instruments: known which will rintegratezthe indications econtinuously :produced :by :two smeasuring instruments,- of the-character of,.a;iflowametersand;.a cchductivitmmetendnathe imanner asst :iorth. above. v .l l isuzansexample, K which iinmo iway'r limitati e, :the "integrating iinstru- Inent rm ay; be 221; sensitive iwattshournneterfhavxingsits potential coilzsuppliediwithza voltagemroportional to :the xindicationvproduced .hy :the ;:flow meter and its -.current rcoil zsnpplied with :.a :cu-r- 'rentproportional etc .-.the :indicatiomproduced by :the. conductivitynneter. 'iThe :rotor-zor :disc :of :the watt -hourzmotercmay :then drive-.themointer vM through reduc-t-ion -gearing. :Ajlternativelmathe flow-' meter may include .a :rota-ry :zelement 1the ispeed -.of which is a proportional .to..the't-.rate -.of

flow of the treated water, andethe currentpassed water to an electricaleconductivity:meterdfiithat 75 rbyzithe conductivitylmetert-mayi'iafter:a nfi tion if required, control the setting of an infinitely variable reduction gear through which the rotary element drives the pointer 2|. Aga n, the flow meter may vary the potential applied to the electrodes of the conductivity meter in accordance with the rate of flow of the water, th current passed through the latter between the electrodes being supplied to the current coil of a sensitive watt-hour meter which has its potential coil supplied from a constant voltage source and the rotor or disc of which drives the pointer 21. Many other examples of suitable arrangements areavailable and the present invention is not concerned with the nature of the integratin instrument as such but merely with the employment of a suitable such instrument in the manner indicated above.

Instead of operating a pointer, or in addition to this, the output of the integrating instrument may displace a member which is associated with control mechanism adapted automatically to supply the required weight of regenerant chemical when a regeneration is carried out. For example, a supply of a solution of the chemical at a standard concentration may be arranged so that it is fed into a stream of water used for regenerating the anion unit under the control of a valve which is opened either automatically or by the operator but is closed automatically when the quantity of concentrated solution delivered corresponds to the setting of the member referred to above. This member may set up a quantity mechanism in the manner usual in commodity meters and a flow meter in the path of the concentrated solution may cause the running down of the mechanism with the closing of the valve when the quantity set up has been supplied. It is thought that this mechanism will be clearly understandable without illustration.

The capacity of anion exchange materials is different for hydrochloric and sulphuric acids so that any change in the chloride/sulphate ratio also affects the period of time between regenerations. In most circumstances, changes in the ratio will be negligible. However, where this does not apply, this ratio may be ascertained from a simple chloride determination and an appropriate correction applied to the indication given by the integrating instrument.

What we claim is:

1. A method of treating water comprisin introducing the water to be treated in a unit containing a cation exchange material, measuring the conductivity of the decationized water, passing the decationized water to a unit containing an anion exchange material, continuously measuring the rate of flow of the water through the latter unit, and, determining the degree of exhaustion of said anion exchange material, the

last step comprising automatically combining th measurement of the conductivity of the decationized water and the indication of the rate of flow through the unit containing the anion exchange material.

2. A method of treating water comprising introducing the water to be treated into a cation unit, passing the decationized water to an anion unit containing anion exchange material, and

determining the degree of exhaustion of said anion exchange material, the last step comprising automatically combining the measurement of the conductivity of the decationized water and the rate of flow of the water through said anion unit.

3. Apparatus for treating water comprising a first unit for receiving the water to be treated, said first unit containing cation exchange material, a second unit in series with said first unit receiving decationized water from said first unit, said second unit containing anion exchange material, a first measuring device disposed between said first and second units adapted to measure the conductivity of the decationized water, a second measuring device located after said second unit and adapted to continuously measure the rate of flow of the water through said second unit, and a third measuring device operatively connected to said first and second measuring devices, adapted to determine the degree of exhaustion of anion exchange material in said second unit, thereby indicating the quantity of regenerate material required by said second uni 4. Apparatus for treating water comprising a cation unit receiving water to be treated, an anion unit containing anion exchange material receiving decationized water from said cation unit, a first indicator operatively associated with said cation unit adapted to measure the conductivity of the decationized water, a second indicator operatively associated with said anion unit adapted to continuously measure the rate of flow of water through said anion unit, and a third indicator operatively connected to said first and second indicators automatically combining the results thereof, thereby determining the degree of exhaustion of said anion exchange material.

' JAMES RATCLIFFE EMME'IT. HENRY ALFRED MATTHEWS.

REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS Number Country Date 437,857 Great Britain Nov. 6, 1935 569,660 Great Britain June 4, 1945 

3. APPARATUS FOR TREATING WATER COMPRISING A FIRST UNIT FOR RECEIVING THE WATER TO BE TREATED, SAID FIRST UNIT CONTAINING CATION EXCHANGE MATERIAL, A SECOND UNIT IN SERIES WITH SAID FIRST UNIT RECEIVING DECATIONIZED WATER FROM SAID FIRST UNIT, SAID SECOND UNIT CONTAINING ANION EXCHANGE MATERIAL, A FIRST MEASURING DEVICE DISPOSE BETWEEN SAID FIRST AND SECOND UNITS ADAPTED TO MEASURE THE CONDUCTIVITY OF THE DECATIONIZED WATER, A SECOND MEASURING DEVICE LOCATED AFTER SAID SECOND UNIT AND ADAPTED TO CONTINUOUSLY MEASURE THE RATE OF FLOW OF THE WATER THROUGH SAID SECOND UNIT, AND A THIRD MEASURING DEVICE OPERATIVELY CONNECTED TO SAID FIRST AND SECOND MEAS- 